How do ISRs notify CUCM that its SIP peering is down and the secondary should be used?

amigan_99 used Ask the Experts™
If I have two SIP routes - model 2951 ISRs CUBE - and you want call manager to
failover if one of them can't complete a call - what is required? We currently have
a SIP trunk to one ISR (and the ISR has a TIP trunk to our call center). For redundancy
we want to add a second ISR/SIP Trunk. But the second should only be used in the
event that the SIP peering on the primary goes down. Advice appreciated.
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Sr. Voice Engineer
Basically, it doesn't. SIP Trunk Status is only know by Call Manager on a call-by-call basis. There is typically no "heatbeat" between a SIP Gateway or CUBE and CUCM. Of course, there is a quasi-heartbeat if SIP Options PINGs are configured.
Example - CUCM sends a SIP INVITE to a SIP Gateway or CUBE. The SIP Trunk is not working for one of various reasons. The SIP Gateway or CUBE returns an error to CUCM and CUCM consults the Route Group to see if there is another Gateway to send the call to. If there is no alternate, a busy signal is generated.
amigan_99Network Engineer


Thanks TIm.

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